Igniter assembly for a gas turbine combustor

ABSTRACT

An igniter assembly for a gas turbine combustor includes a first electrode, a second electrode, and an insulator. The first electrode, the second electrode, and the insulator form a cavity, the second electrode forms an outlet passage extending from the cavity, a maximum cross-sectional area of the cavity is greater than a cross-sectional area of the outlet passage, and the cross-sectional area of the outlet passage is substantially constant along a longitudinal extent of the outlet passage. In addition, the first electrode and the second electrode are configured to ionize gas within the cavity in response to an electrical current applied to the first electrode or to the second electrode.

BACKGROUND

The subject matter disclosed herein relates to an igniter assembly for agas turbine combustor.

Gas turbine engines typically include a combustor configured to igniteand combust a fuel-air mixture, thereby generating pressurized exhaustgas. The pressurized exhaust gas may be used to drive a turbine rotor torotate, and the turbine rotor, in turn, may drive a compressor rotor torotate (e.g., via a shaft coupled to the turbine rotor and thecompressor rotor). Rotation of the compressor rotor may generatepressurized air, which may be combined with fuel and provided to thecombustor for ignition and combustion.

The fuel-air mixture within the combustor is typically ignited by one ormore igniter assemblies in fluid communication with an interior of thecombustor. Certain igniter assemblies include electrodes configured toionize gas in response to an electrical current applied to one of theelectrodes. The ionized gas (e.g., plasma) is emitted from the igniterassembly and ignites the fuel-air mixture within the interior of thecombustor. To facilitate interaction between the ionized gas emittedfrom the igniter assembly and the fuel-air mixture, the tip of theigniter assembly, which emits the ionized gas, it typically positionedproximate to the combustion zone within the interior of the combustor.However, when the combustor is operated at higher temperatures, the tipof the igniter assembly may wear, thereby increasing the frequency ofmaintenance operations (e.g., removal and replacement of the igniterassembly).

BRIEF DESCRIPTION

In one embodiment, an igniter assembly for a gas turbine combustorincludes a first electrode, a second electrode, and an insulator. Thefirst electrode, the second electrode, and the insulator form a cavity,the second electrode forms an outlet passage extending from the cavity,a maximum cross-sectional area of the cavity is greater than across-sectional area of the outlet passage, a first longitudinal end ofthe outlet passage is positioned at an interface between the outletpassage and the cavity, a second longitudinal end of the outlet passageis positioned at a tip of the igniter assembly, and the cross-sectionalarea of the outlet passage is substantially constant along alongitudinal extent of the outlet passage between the first longitudinalend and the second longitudinal end. In addition, the first electrodeand the second electrode are configured to ionize gas within the cavityin response to an electrical current applied to the first electrode orto the second electrode.

In another embodiment, a combustor for a gas turbine system includes acombustor casing having an interior-establishing wall, and a chamberextending to the interior-establishing wall. In addition, the combustorincludes an igniter assembly disposed within the chamber such that a tipof the igniter assembly is positioned radially outwardly from theinterior-establishing wall. The igniter assembly includes a firstelectrode, a second electrode, and an insulator. In addition, the firstelectrode, the second electrode, and the insulator form a cavity, thesecond electrode forms an outlet passage extending from the cavity, amaximum cross-sectional area of the cavity is greater than a minimumcross-sectional area of the outlet passage, and the first electrode andthe second electrode are configured to ionize gas within the cavity inresponse to an electrical current applied to the first electrode or tothe second electrode.

In a further embodiment, an igniter assembly for a gas turbine combustorincludes a first electrode, a second electrode, and an insulator. Thefirst electrode, the second electrode, and the insulator form a cavity,the second electrode forms an outlet passage extending from the cavity,a maximum cross-sectional area of the cavity is greater than a minimumcross-sectional area of the outlet passage, the cavity includes a firstportion having a cross-sectional area that decreases between the maximumcross-sectional area of the cavity and the outlet passage, the cavityincludes a second portion extending from the first electrode to thefirst portion and having a substantially constant cross-sectional areasubstantially equal to the maximum cross-sectional area of the cavity,and the second portion is formed only by the insulator and the firstelectrode. In addition, the outlet passage is the only fluid passageextending from the cavity, and the first electrode and the secondelectrode are configured to ionize gas within the cavity in response toan electrical current applied to the first electrode or to the secondelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a gas turbine system,including an igniter assembly configured to initiate combustion of afuel-air mixture within a combustor;

FIG. 2 is a cross-sectional view of an embodiment of a combustor thatmay be used within the gas turbine system of FIG. 1, including anembodiment of an igniter assembly;

FIG. 3 is a schematic diagram of an embodiment of a combustor having arecessed igniter assembly;

FIG. 4 is a cross-sectional view of an embodiment of an igniter assemblythat may be used in the combustor of FIG. 2 and/or in the combustor ofFIG. 3; and

FIG. 5 is a cross-sectional view of another embodiment of an igniterassembly that may be used in the combustor of FIG. 2 and/or in thecombustor of FIG. 3.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, all features ofan actual implementation may not be described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments disclosed herein, thearticles “a,” “an,” “the,” and “said” are intended to mean that thereare one or more of the elements. The terms “comprising,” “including,”and “having” are intended to be inclusive and mean that there may beadditional elements other than the listed elements.

Embodiments disclosed herein may enhance gas turbine engine operation byproviding an igniter assembly configured to generate an ionized gasplume that has a greater propagation distance than the ionized gas plumefrom a typical igniter assembly, thereby enabling a tip of the igniterassembly to be positioned farther from a combustion zone within thecombustor. For example, in certain embodiments, the igniter assemblyincludes a first electrode (e.g., center electrode), a second electrode(e.g., outer shell electrode), and an insulator. The first electrode,the second electrode, and the insulator form a cavity, and the secondelectrode forms an outlet passage extending from the cavity. A maximumcross-sectional area of the cavity is greater than a minimumcross-sectional area of the outlet passage. In addition, the firstelectrode and the second electrode are configured to ionize gas withinthe cavity and, in certain embodiments, within the outlet passage inresponse to an electrical current applied to the first electrode or tothe second electrode. The ionization of the gas within the cavityinduces the gas to expand. Because the minimum cross-sectional area ofthe outlet passage is less than the maximum cross-sectional area of thecavity, expansion of the gas within the cavity increases the fluidpressure within the cavity. The fluid pressure drives the ionized gasthrough the outlet passage at a velocity greater than the velocity ofgas flowing through an outlet passage having a minimum cross-sectionalarea equal to or greater than the maximum cross-sectional area of thecavity. Accordingly, a plume having a greater propagation distance isgenerated (e.g., as compared to a plume generated by an igniter assemblythat receives a substantially equal electrical energy input and has anoutlet passage with a minimum cross-sectional area equal to or greaterthan the maximum cross-sectional area of the cavity). The greater plumepropagation distance enables the tip of the igniter assembly to bepositioned farther from the combustion zone within the combustor,thereby reducing wear on the igniter assembly. As a result, thefrequency of maintenance operations may be reduced. In addition, thegreater plume propagation distance may increase the likelihood ofignition of the fuel-air mixture, thereby enhancing the capabilities ofthe gas turbine system. Furthermore, the capability of generating aplume having a greater propagation distance for a particular energyinput may enable the igniter assembly to utilize less energy if ashorter plume is desired.

Turning now to the drawings, FIG. 1 is a block diagram of an embodimentof a turbine system 10 (e.g., gas turbine system, turbine engine, gasturbine engine), including an igniter assembly configured to initiatecombustion of a fuel-air mixture within a combustor. The turbine system10 includes a fuel nozzle/injector 12, a fuel supply 14, and a combustor16. As illustrated, the fuel supply 14 routes a liquid fuel and/or gasfuel, such as jet fuel, to the gas turbine system 10 through the fuelinjector 12 into the combustor 16. As discussed below, the fuel injector12 is configured to inject and mix the fuel with compressed air. Thecombustor 16 ignites and combusts the fuel-air mixture, and then passeshot pressurized exhaust gas into a turbine 18. The turbine 18 includesone or more stators having fixed vanes or blades, and one or more rotorshaving blades that rotate relative to the stators. The exhaust gaspasses through the turbine rotor blades, thereby driving the turbinerotor to rotate. Coupling between the turbine rotor and a shaft 19induces rotation of the shaft 19, which is also coupled to severalcomponents throughout the gas turbine system 10, as illustrated.Eventually, the exhaust of the combustion process exits the gas turbinesystem 10 via an exhaust outlet 20.

A compressor 22 includes blades rigidly mounted to a rotor, which isdriven to rotate by the shaft 19. As air passes through the rotatingblades, air pressure increases, thereby providing the combustor 16 withsufficient air for proper combustion. The compressor 22 intakes air tothe gas turbine system 10 via an air intake 24. Further, the shaft 19may be coupled to a load 26, which is powered via rotation of the shaft19. As will be appreciated, the load 26 may be any suitable device thatmay use the power of the rotational output of the gas turbine system 10,such as a power generation plant or an external mechanical load. Forexample, the load 26 may include an electrical generator, a propeller ofan airplane, and so forth. The air intake 24 draws air 30 into the gasturbine system 10 via a suitable mechanism, such as a cold air intake.The air 30 then flows through blades of the compressor 22, whichprovides compressed air 32 to the combustor 16. For example, the fuelinjector 12 may inject the compressed air 32 and fuel 14, as a fuel-airmixture 33, into the combustor 16. Alternatively, the compressed air 32and fuel 14 may be injected directly into the combustor for mixing andcombustion.

In the illustrated embodiment, the combustor 16 includes an igniterassembly 34 configured to initiate combustion of the fuel-air mixture.In certain embodiments, the igniter assembly 34 includes a firstelectrode (e.g., center electrode), a second electrode (e.g., outershell electrode), and an insulator. The first electrode, the secondelectrode, and the insulator form a cavity, and the second electrodeforms an outlet passage extending from the cavity. The first electrodeand the second electrode are configured to ionize gas within the cavityand, in certain embodiments, within the outlet passage in response to anelectrical current applied to the first electrode or to the secondelectrode. The ionized gas flows from the outlet passage and forms aplume extending into a combustion zone within the combustor. The plumeignites the fuel-air mixture, thereby facilitating combustion within thecombustor 16.

FIG. 2 is a cross-sectional view of an embodiment of a combustor 16 thatmay be used within the gas turbine system of FIG. 1, including anembodiment of an igniter assembly 34. As illustrated, the combustor 16includes fuel nozzles 12 that are attached to an end cover 46 at a baseof the combustor 16. In certain embodiments, the combustor 16 mayinclude five or six fuel nozzles 12. In other embodiments, the combustor16 may include a single large fuel nozzle 12. The surfaces and geometryof the fuel nozzles 12 are particularly configured to enhance mixing ofthe air and fuel as the fuel-air mixture flows downstream through thecombustor 16. The enhanced mixing may increase combustor efficiency,thereby producing more power in the turbine engine. The fuel-air mixtureis expelled from the fuel nozzles 12 in a downstream direction 48 to acombustion zone 50 inside a combustor casing 52.

In the illustrated embodiment, the combustion zone 50 is located insidethe combustor casing 52, downstream from the fuel nozzles 12 andupstream from a transition piece 54, which directs the pressurizedexhaust gas toward the turbine 18. The transition piece 54 includes aconverging section configured to increase a velocity of the exhaust gas,thereby producing a greater force to drive the turbine rotor inrotation. In the illustrated embodiment, the combustor 16 includes aliner 56 located inside the casing 52 to provide a hollow annular path58 for a cooling airflow 60, which cools the casing 52 around thecombustion zone 50. As illustrated, the cooling airflow 60 flows in anupstream direction 62, opposite the downstream direction 48, through thehollow annular path 58 to the fuel nozzles 12. The airflow 60 then mixeswith the fuel to establish a fuel-air mixture suitable for combustion.In certain embodiments, the liner 56 includes cooling holes configuredto facilitate passage of the cooling airflow into an interior of thecombustor, thereby cooling the liner 56 and/or providing additional airfor combustion. Furthermore, the liner 56 may establish a suitable shapeto improve flow from the fuel nozzles 12 to the turbine 18.

In the illustrated embodiment, the combustor 16 includes an igniterassembly 34 configured to initiate combustion of the fuel-air mixture.The igniter assembly 34 extends through the casing 52, and an opening inthe liner 56 enables a plume of ionized gas from the igniter assembly 34to extend into the combustion zone 50. The plume ignites the fuel-airmixture, thereby establishing flames 64 within the combustor 16. Asdiscussed in detail below, the igniter assembly 34 generates a plumehaving a greater propagation distance than plumes generated by typicaligniter assemblies, thereby enabling the tip of the igniter assembly tobe positioned farther from the combustion zone 50. As a result, wear onthe igniter assembly may be reduced, thereby reducing the frequency ofmaintenance operations on the gas turbine system (e.g., replacing theigniter assembly). In addition, the greater plume propagation distancemay increase the likelihood of ignition of the fuel-air mixture, therebyenhancing the capabilities of the gas turbine system. While theillustrated combustor 16 includes one igniter assembly 34, it should beappreciated that in alternative embodiments, the combustor may includeadditional igniter assemblies, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ormore igniter assemblies.

FIG. 3 is a schematic diagram of an embodiment of a combustor 16 havinga recessed igniter assembly 34. In certain embodiments, the igniterassembly 34 includes a first electrode (e.g., center electrode), asecond electrode (e.g., outer shell electrode), and an insulator. Thefirst electrode, the second electrode, and the insulator form a cavity,and the second electrode forms an outlet passage extending from thecavity. A maximum cross-sectional area of the cavity is greater than aminimum cross-sectional area of the outlet passage. In addition, thefirst electrode and the second electrode are configured to ionize gaswithin the cavity and, in certain embodiments, within the outlet passagein response to an electrical current applied to the first electrode orto the second electrode. The ionization of the gas within the cavityinduces the gas to expand. Because the minimum cross-sectional area ofthe outlet passage is less than the maximum cross-sectional area of thecavity, expansion of the gas within the cavity increases the fluidpressure within the cavity. The fluid pressure drives the ionized gasthrough the outlet passage at a velocity greater than the velocity ofgas flowing through an outlet passage having a minimum cross-sectionalarea equal to or greater than the maximum cross-sectional area of thecavity. Accordingly, a plume 66 of ionized gas having a greaterpropagation distance is generated (e.g., as compared to a plumegenerated by an igniter assembly that receives a substantially equalelectrical energy input and has an outlet passage with a minimumcross-sectional area equal to or greater than the maximumcross-sectional area of the cavity). The greater plume propagationdistance enables a tip 68 of the igniter assembly 34 to be positionedfarther from the combustion zone 50 within the combustor 16, therebyreducing wear on the igniter assembly. As a result, the frequency ofmaintenance operations (e.g., replacement of the igniter assembly) maybe reduced. In addition, the greater plume propagation distance mayincrease the likelihood of ignition of the fuel-air mixture, therebyenhancing the capabilities of the gas turbine system. Furthermore, thecapability of generating a plume having a greater propagation distancefor a particular energy input may enable the igniter assembly to utilizeless energy if a shorter plume is desired.

As illustrated, the igniter assembly 34 is disposed within a chamber 67that is in fluid communication with an interior (e.g., combustion zone50) of the combustor 16. In the illustrated embodiment, the chamber 67extends to the liner 56 (e.g., interior-establishing wall of thecombustor). However, it should be appreciated that in alternativeembodiments, the chamber may extend to another structure thatestablishes the interior of the combustor. For example, in certainembodiments, the liner may be omitted, and the chamber may extend toanother interior-establishing wall of the combustor casing. Thedimensions of the chamber 67 may be particularly selected to accommodatethe igniter assembly 34 and to enable the tip 68 of the igniter assembly34 to be positioned radially outwardly (e.g., recessed within thechamber) from the liner/interior-establishing wall of the combustor.

In certain embodiments, a propagation distance 70 of the plume 66 fromthe illustrated igniter assembly 34 may be between about 10 mm and about30 mm, about 11 mm and about 27 mm, or about 12 mm and about 25 mm. Byway of further example, the propagation distance 70 of the plume 66 maybe greater than 10 mm, greater than 12 mm, greater than 15 mm, greaterthan 20 mm, or greater than 25 mm. In contrast, the plume propagationdistance from a typical igniter may be about 6 mm.

Due to the greater plume propagation distance 70, the tip 68 of theigniter assembly 34 may be positioned a distance 72 radially outwardlyfrom the combustor liner/interior-establishing wall of the combustor(e.g., recessed within the chamber). The recess distance 72 may be abouthalf the propagation distance 70 of the plume 66. For example, if thepropagation distance 70 of the plume 66 is about 24 mm, the recessdistance 72 may be about 12 mm. Accordingly, the tip 68 of the igniterassembly 34 may be positioned about 12 mm from theliner/interior-establishing wall of the combustor 16, thereby reducingwear on the igniter assembly 34 (e.g., as compared to a typical igniterthat generates a plume having a 6 mm propagation distance, in which thetip is positioned radially inward of the combustorliner/interior-establishing wall). In further embodiments, the recessdistance 72 may be between about 0 mm and about 15 mm, about 0 mm andabout 13 mm, about 1 mm and about 12 mm, or about 2 mm and about 12 mm.By way of further example, the recess distance 72 may be greater than 1mm, greater than 3 mm, greater than 5 mm, greater than 7 mm, greaterthan 9 mm, or greater than 11 mm.

Furthermore, if the recess distance 72 is about half of the propagationdistance 70 of the plume 66, an impingement distance 74 of the plume 66into the interior (e.g., combustion zone 50) of the combustor 16 may beabout half of the propagation distance 70 of the plume 66. For example,if the propagation distance 70 of the plume 66 is about 24 mm, theimpingement distance 74 may be about 12 mm. Accordingly, the likelihoodof igniting the fuel-air mixture may be increased (e.g., as compared toan igniter having a tip positioned at the liner/interior-establishingwall and configured to produce a plume having a 6 mm propagationdistance). For example, the plume may extend beyond a boundary layer onthe surface of the liner/interior-establishing wall and into arecirculation portion of the combustion zone. As a result, thecapabilities of the gas turbine system may be enhanced (e.g., byenhancing the re-light capabilities of the combustor while the fuel-airmixture is lean). While the recess distance 72 and the complementaryimpingement distance 74 are about half the propagation distance 70 ofthe plume 66 in the illustrated embodiment, it should be appreciatedthat in alternative embodiments, the recess distance 72 or theimpingement distance 74 may be between about 10 percent and about 90percent, about 20 percent and about 80 percent, about 30 percent andabout 70 percent, or about 40 percent and about 60 percent of thepropagation distance of the plume. As used herein, “propagationdistance” refers to the distance between the tip 68 of the igniterassembly 34 and the tip of the plume 66, and the tip of the plume 66refers to the point along the length of the plume where the temperaturedrops below 1500 K. Furthermore, as used herein, “impingement distance”refers to the distance between the combustor liner/interior-establishingwall of the combustor and the tip of the plume 66.

FIG. 4 is a cross-sectional view of an embodiment of an igniter assembly34 that may be used in the combustor of FIG. 2 and/or in the combustorof FIG. 3. In the illustrated embodiment, the igniter assembly 34includes a first electrode, such as the illustrated center electrode 76,a second electrode, such as the illustrated outer shell electrode 78,and an insulator 80. As illustrated, the outer shell electrode 78 isdisposed about the center electrode 76, and the insulator 80 is disposedradially between the center electrode 76 and the outer shell electrode78. In certain embodiments, the igniter assembly 34 is circularlysymmetric about a central axis 82. In such embodiments, the igniterassembly 34 may have a circular cross-section within a plane extendingperpendicularly to the central axis 82. In addition, the insulator 80and the outer shell electrode 78 extend about the center electrode 76along a circumferential axis 84, and the insulator 80 is disposedbetween the center electrode 76 and the outer shell electrode 78 along aradial axis 86. While the first electrode includes a single centerelectrode in the illustrated embodiment, it should be appreciated thatin alternative embodiments the first electrode may be positionedoff-center relative to the central axis and/or may include multipleseparate electrodes. In addition, while the second electrode is a singleouter shell electrode in the illustrated embodiment, it should beappreciated that in alternative embodiments, the second electrode maynot extend about the first electrode and/or may include multipleseparate electrodes.

In the illustrated embodiment, the center electrode 76, the outer shellelectrode 78, and the insulator 80 form a cavity 88, and the outer shellelectrode 78 forms an outlet passage 90 extending from the cavity 88.Indeed, in the illustrated embodiment, the outlet passage 90 is formedonly by the outer shell electrode 78. As illustrated, the cavity 88 ispositioned between the center electrode 76 and the outlet passage 90along a longitudinal axis 92.

In the illustrated embodiment, a maximum diameter 93 of the cavity 88 isgreater than a minimum diameter 94 of the outlet passage 90.Accordingly, a maximum cross-sectional area of the cavity 88 (e.g., areaof the cross-section extending within a plane perpendicular to thecentral axis 82) is greater than a minimum cross-sectional area of theoutlet passage 90 (e.g., area of the cross-section extending within aplane perpendicular to the central axis 82). The center electrode 76 andthe outer shell electrode 78 are configured to ionize gas within thecavity 88 and, in certain embodiments, within the outlet passage 90 inresponse to an electrical current applied to the center electrode 76 orthe outer shell electrode 78. The ionization of the gas within thecavity 88 induces the gas to expand. Because the minimumdiameter/cross-sectional area of the outlet passage 90 is less than themaximum diameter/cross-sectional area of the cavity 88, expansion of thegas within the cavity 88 increases the fluid pressure within the cavity88. The fluid pressure drives the ionized gas through the outlet passage90 at a velocity greater than the velocity of gas flowing through anoutlet passage having a minimum diameter/cross-sectional area equal toor greater than a maximum diameter/cross-sectional area of the cavity.Accordingly, a plume having a greater propagation distance is generated(e.g., as compared to a plume generated by an igniter assembly thatreceives a substantially equal electrical energy input and has an outletpassage with a minimum diameter/cross-sectional area equal to or greaterthan the maximum diameter/cross-sectional area of the cavity). Thegreater plume propagation distance enables the tip of the igniterassembly to be positioned farther from the combustion zone within theinterior of the combustor, thereby reducing wear on the igniterassembly. As a result, the frequency of maintenance operations (e.g.,replacing the igniter assembly) may be reduced. In addition, the greaterplume propagation distance may increase the likelihood of ignition ofthe fuel-air mixture, thereby enhancing the capabilities of the gasturbine system. Furthermore, the capability of generating a plume havinga greater propagation distance for a particular energy input may enablethe igniter assembly to utilize less energy if a shorter plume isdesired.

As illustrated, the cavity 88 includes a first portion 96 having adiameter/cross-sectional area that decreases between the maximumdiameter/cross-sectional area 93 of the cavity 88 and the outlet passage90 (e.g., an interface 97 between the cavity 88 and the outlet passage90). In the illustrated embodiment, the first portion 96 of the cavity88 is formed only by the outer shell electrode 78. However, inalternative embodiments, the first portion may be formed only by theinsulator, or the first portion may be formed by the insulator and theouter shell electrode. In addition, the cavity 88 includes a secondportion 98 extending from the center electrode 76 to the first portion96. In the illustrated embodiment, the second portion 98 of the cavity88 is formed only by the insulator 80 and the center electrode 76.However, in alternative embodiments, the second portion may be formed bythe insulator, the center electrode, and the outer shell electrode. Theinterface 99 between the first portion 96 and the second portion 98 islocated at the point of maximum diameter/cross-sectional area closest tothe outlet passage 90 along the longitudinal axis 92.

In the illustrated embodiment, the second portion 98 of the cavity 88has a substantially constant diameter/cross-sectional area, which isequal to the maximum diameter/cross-sectional area of the cavity 88.However, it should be appreciated that in alternative embodiments, thesecond portion of the cavity may have other suitable shapes. Forexample, the second portion may include one or more diverging sections,one or more converging sections, one or more substantially constantdiameter/cross-sectional area sections, or a combination thereof.Furthermore, in the illustrated embodiment, the diameter of the firstportion 96 decreases substantially linearly between the maximum diameter93 of the cavity 88 and the outlet passage 90 (e.g., the interface 97between the cavity 88 and the outlet passage 90). However, it should beappreciated that in alternative embodiments, the first portion of thecavity may have other suitable shapes. For example, the diameter of thefirst portion may decrease along a curved path between the maximumdiameter of the cavity and the outlet passage, the first portion mayinclude one or more substantially constant diameter/cross-sectional areasections, the first portion may include one or more diverging sections,or a combination thereof. As used herein with reference to the firstportion, “decrease” refers to a net decrease in diameter/cross-sectionalarea between the maximum diameter/cross-sectional area of the cavity(e.g., at the interface 99) and the outlet passage (e.g., at theinterface 97). Accordingly, the diameter/cross-sectional area of thefirst portion may vary locally (e.g., increase and decrease) between themaximum diameter/cross-sectional area of the cavity (e.g., at theinterface) and the outlet passage, such that thediameter/cross-sectional area of the first portion at the outlet passageis less than the maximum diameter/cross-sectional area of the cavity.

In the illustrated embodiment, a first longitudinal end 101 of theoutlet passage 90 is positioned at the interface 97 between the outletpassage 90 and the cavity 88. In addition, a second longitudinal end 103of the outlet passage 90 is positioned at the tip 68 of the igniterassembly 34. The diameter/cross-sectional area of the outlet passage 90is substantially constant and equal to the minimum diameter94/cross-sectional area of the outlet passage 90 between the firstlongitudinal end 101 and the second longitudinal end 103. Because thediameter/cross-sectional area of the outlet passage is substantiallyconstant, the manufacturing process of the igniter assembly may be lesstime-consuming and/or less expensive than the manufacturing process ofan igniter assembly having converging and/or diverging section(s).However, it should be appreciated that in alternative embodiments, theoutlet passage may include one or more diverging sections, one or moreconverging sections, one or more substantially constantdiameter/cross-sectional area sections, or a combination thereof. Forexample, the outlet passage may include a constantdiameter/cross-sectional area section and a diverging section, and theconstant diameter/cross-sectional area section may be positioned betweenthe cavity and the diverging section.

In certain embodiments, the maximum diameter 93 of the cavity 88 may beabout 1.5 times greater than the minimum diameter 94 of the outletpassage 90. In such embodiments, the maximum cross-sectional area of thecavity may be more than two times greater than the minimumcross-sectional area of the outlet passage. This configuration mayestablish a fluid pressure of at least 5 atm within the cavity 88,thereby facilitating the establishment of a plume having a targetpropagation distance (e.g., about 12 mm to about 24 mm). By way ofexample, the maximum diameter 93 of the cavity 88 may be about 6 mm, andthe minimum diameter 94 of the outlet passage 90 may be about 4 mm.However, it should be appreciated that the maximum diameter 93 of thecavity 88, the minimum diameter 94 of the outlet passage 90, the maximumcross-sectional area of the cavity 88, the minimum cross-sectional areaof the outlet passage 90, or a combination thereof, may be particularlyselected to achieve a target fluid pressure within the cavity 88 and/ora target plume propagation distance, among other target operatingparameters of the igniter assembly. For example, in certain embodiments,the maximum diameter of the cavity may be between about 1.05 and about3, about 1.1 and about 2.5, about 1.2 and about 2, about 1.3 and about1.8, or about 1.4 and about 1.6 times greater than the minimum diameterof the outlet passage. Furthermore, in certain embodiments, the maximumcross-sectional area of the cavity may be about 1.1 and about 10, about1.5 and about 8, about 2 and about 6, about 2 and about 5, or about 2and about 3 times greater than the minimum cross-sectional area of theoutlet passage. By way of further example, the maximum cross-sectionalarea of the cavity may be more than 2, 3, 4, 5, 6, 7, 8, or 9 timesgreater than the minimum cross-sectional area of the outlet passage.Furthermore, in certain embodiments, the maximum diameter 93 of thecavity 88 may be between about 1 mm and about 20 mm, about 2 mm andabout 15 mm, about 4 mm and about 10 mm, about 5 mm and about 7 mm, orabout 6 mm. In addition, in certain embodiments, the minimum diameter 94of the outlet passage 90 may be between about 1 mm and about 15 mm,about 2 mm and about 12 mm, about 3 mm and about 10 mm, about 4 mm andabout 6 mm, or about 4 mm and about 5 mm. While the target pressurewithin the cavity is at least 5 atm in certain embodiments, it should beappreciated that in other embodiments, the target pressure within thecavity may be at least 2 atm, at least 3 atm, at least 4 atm, at least 5atm, at least 6 atm, at least 7 atm, at least 8 atm, at least 9 atm, atleast 10 atm, or more.

In the illustrated embodiment, a longitudinal extent 100 of the cavity88 (e.g., the extent of the cavity along the longitudinal axis 92) isgreater than a longitudinal extent 102 of the outlet passage 90 (e.g.,the extent of the outlet passage along the longitudinal axis 92). Forexample, in certain embodiments, the longitudinal extent 100 of thecavity 88 may be about twice the longitudinal extent 102 of the outletpassage 90. By way of further example, the longitudinal extent 100 ofthe cavity 88 may be between about 0.5 and about 10, about 1.0 and about8.0, about 1.5 and about 7.0, about 2.0 and about 5.0, or about 2.0 andabout 3.0 times longer than the longitudinal extent 102 of the outletpassage 90. In certain embodiments, the longitudinal extent 100 of thecavity 88 may be between about 1 mm and about 10 mm, about 2 mm andabout 8 mm, about 3 mm and about 7 mm, or about 4 mm and about 6 mm. Forexample, the longitudinal extent 100 of the cavity 88 may be about 2.1mm, about 3 mm, about 7.1 mm, or about 8 mm. In addition, thelongitudinal extent 102 of the outlet passage 90 may be between about0.5 mm and about 5 mm, about 0.75 mm and about 4 mm, or about 1 mm andabout 3 mm. For example, the longitudinal extent 102 of the outletpassage 90 may be about 0.9 mm or about 2.9 mm. The longitudinal extentof the cavity and the longitudinal extent of the outlet passage may beparticularly selected to achieve a target pressure within the cavityand/or to establish a target plume propagation distance, among othertarget operating parameters of the igniter assembly.

In the illustrated embodiment, the outlet passage 90 is the only fluidpassage extending from the cavity 88. Accordingly, gas and, in certainembodiments, liquid droplets from the interior of the combustor (e.g.,fuel, air, combustion products, exhaust gas, etc.) may enter the cavity88 via the outlet passage 90. In response to applying an electricalcurrent to the center electrode 76 or to the outer shell electrode 78,the gas within the cavity 88 may be ionized and, in certain embodiments,the liquid droplets within the cavity 88 may be vaporized and ionized.The ionization of the gas within the cavity 88 may induce the ionizedgas to expand. Because the minimum diameter/cross-sectional area of theoutlet passage is less than the maximum diameter/cross-sectional area ofthe cavity, expansion of the gas within the cavity increases the fluidpressure within the cavity 88, and the fluid pressure drives the ionizedgas through the outlet passage 90. While the igniter assembly includes asingle fluid passage extending to/from the cavity in the illustratedembodiment, it should be appreciated that in alternative embodiments,multiple fluid passages may extend to/from the cavity. For example, incertain embodiments, the igniter assembly may have an inlet configuredto receive gas for ionization.

As previously discussed, in certain embodiments, the igniter assemblyhas a substantially circular cross-sectional shape (e.g., shape of thecross-section within a plane extending perpendicularly to the centralaxis 82). Accordingly, each of the center electrode, the outer shellelectrode, and the insulator may have a substantially circularcross-sectional shape. In addition, in certain embodiments, each of thecavity and the outlet passage may have a substantially circularcross-sectional shape. However, it should be appreciated that inalternative embodiments, the cavity and/or the outlet passage may haveanother suitable cross-sectional shape, such as elliptical or polygonal,among other suitable shapes. Furthermore, in certain embodiments, thecenter electrode, the outer shell electrode, the insulator, or acombination thereof may have other suitable cross-sectional shapes. Forexample, at least one of the center electrode, the insulator, and theouter shell electrode may have an elliptical or polygonalcross-sectional shape, or another suitable cross-sectional shape.Furthermore, the radially inward surface of the insulator and/or theouter shell electrode may have a cross-sectional shape corresponding tothe cross-sectional shape of the cavity, and/or the radially inwardsurface of the outer shell electrode may have a cross-sectional shapecorrespond to the cross-sectional shape of the outlet passage. As usedherein, “cross-sectional area” refers to the area of the cross-sectionof the cavity/outlet passage within a plane extending perpendicularly tothe central axis 82, regardless of the cross-sectional shape of thecavity/outlet passage.

FIG. 5 is a cross-sectional view of another embodiment of an igniterassembly 104 that may be used in the combustor of FIG. 2 and/or in thecombustor of FIG. 3. In the illustrated embodiment, the igniter assembly104 includes a center electrode 106, an outer shell electrode 108disposed about the center electrode 106, and an insulator 110 disposedbetween the center electrode 106 and the outer shell electrode 108. Inthe illustrated embodiment, the center electrode 106, the outer shellelectrode 108, and the insulator 110 form a cavity 112, and the outershell electrode 108 forms an outlet passage 114 extending from thecavity 112. As illustrated, the cavity 112 is positioned between thecenter electrode 106 and the outlet passage 114 along the longitudinalaxis 92.

In the illustrated embodiment, a maximum diameter 116 of the cavity 112is greater than a minimum diameter 118 of the outlet passage 114.Accordingly, a maximum cross-sectional area of the cavity 112 (e.g.,area of the cross-section extending within a plane perpendicular to thecentral axis 82) is greater than a minimum cross-sectional area of theoutlet passage 114 (e.g., area of the cross-section extending within aplane perpendicular to the central axis 82). The center electrode 106and the outer shell electrode 108 are configured to ionize gas withinthe cavity 112 and, in certain embodiments, within the outlet passage114 in response to an electrical current applied to the center electrode106 or to the outer shell electrode 108.

As illustrated, the cavity 112 includes a first portion 120 having adiameter/cross-sectional area that decreases between the maximumdiameter/cross-sectional area 116 of the cavity 112 and the outletpassage 114. In the illustrated embodiment, the first portion 120 of thecavity 112 is formed only by the outer shell electrode 108. In addition,the cavity 112 includes a second portion 122 extending between thecenter electrode 106 and the first portion 120. In the illustratedembodiment, the second portion 122 of the cavity 112 is formed by theinsulator 110 and the center electrode 106. The interface 123 betweenthe first portion 120 and the second portion 122 is located at the pointof maximum diameter/cross-sectional area closest to the outlet passage114 along the longitudinal axis 92.

In the illustrated embodiment, a longitudinal extent 124 of the firstportion 120 (e.g., extent of the first portion 120 along thelongitudinal axis 92) is about 1 mm. However, it should be appreciatedthat in alternative embodiments, the longitudinal extent 124 of thefirst portion 120 may be between about 0.1 mm and about 10 mm, about 1mm and about 8 mm, about 2 mm and about 6 mm, or about 2 mm and about 4mm. For example, the longitudinal extent 124 of the first portion 120may be about 0.1 mm or about 1 mm. In addition, a longitudinal extent126 of the second portion 122 (e.g., extent of the second portion 122along the longitudinal axis 92) is about 7 mm. However, it should beappreciated that in alternative embodiments, the longitudinal extent 126of the second portion 122 may be between about 1 mm and about 10 mm,about 2 mm and about 8 mm, about 3 mm and about 7 mm, or about 5 mm andabout 7 mm. For example, the longitudinal extent 126 of the secondportion 122 may be about 2 mm or about 7 mm. In addition, in certainembodiments, the longitudinal extent 126 of the second portion 122 maybe between about 0.5 and about 10, about 1 and about 7, about 1.6 andabout 6, or about 2 and about 5 times greater than the longitudinalextent 124 of the first portion 120. The longitudinal extent of thefirst portion, the longitudinal extent of the second portion, themaximum diameter/cross-sectional area of the cavity, the minimumdiameter/cross-sectional area of the outlet passage, the shape of thefirst portion of the cavity (e.g., cross-sectional shape, profile,etc.), the shape of the second portion of the cavity (e.g.,cross-sectional shape, profile, etc.), the shape of the outlet passage(e.g., cross-sectional shape, profile, etc.), or a combination thereof,may be particularly selected to achieve a target pressure within thecavity and/or to establish a target plume propagation distance, amongother target operating parameters of the igniter assembly.

This written description uses examples to disclose the igniter assembly,including the best mode, and also to enable any person skilled in theart to practice the igniter assembly, including making and using anydevices or systems and performing any incorporated methods. Thepatentable scope of the igniter assembly is defined by the claims, andmay include other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

The invention claimed is:
 1. An igniter assembly for a gas turbinecombustor, comprising: a first electrode, a second electrode, and aninsulator, wherein the first electrode, the second electrode, and theinsulator form a cavity, the second electrode forms an outlet passageextending from the cavity, a maximum cross-sectional area of the cavityis greater than a cross-sectional area of the outlet passage, a firstlongitudinal end of the outlet passage is positioned at an interfacebetween the outlet passage and the cavity, a second longitudinal end ofthe outlet passage is positioned at a tip of the igniter assembly, thecavity includes a converging section extending to the interface with theoutlet passage, and the cross-sectional area of the outlet passage issubstantially constant along a longitudinal extent of the outlet passagebetween the first longitudinal end and the second longitudinal end;wherein the cavity includes a first portion forming the convergingsection, the first portion has a cross-sectional area that decreasesbetween the maximum cross-sectional area of the cavity and the interfacewith the outlet passage, and the first portion is formed only by thesecond electrode; wherein the cavity includes a second portion having asubstantially constant cross-sectional area substantially equal to themaximum cross-sectional area of the cavity, and the second portion isformed only by the insulator and the first electrode; and wherein thefirst electrode and the second electrode are configured to ionize gaswithin the cavity in response to an electrical current applied to thefirst electrode or to the second electrode.
 2. The igniter assembly ofclaim 1, wherein a longitudinal extent of the cavity is greater than thelongitudinal extent of the outlet passage.
 3. The igniter assembly ofclaim 2, wherein the longitudinal extent of the cavity is about twicethe longitudinal extent of the outlet passage.
 4. The igniter assemblyof claim 1, wherein the first electrode comprises a center electrode,the second electrode comprises an outer shell electrode disposedcircumferentially about the center electrode, and the insulator isdisposed radially between the center electrode and the outer shellelectrode.
 5. The igniter assembly of claim 1, wherein the maximumcross-sectional area of the cavity is more than two times greater thanthe cross-sectional area of the outlet passage.
 6. The igniter assemblyof claim 1, wherein the outlet passage is the only fluid passageextending from the cavity.
 7. An igniter assembly for a gas turbinecombustor, comprising: a first electrode, a second electrode, and aninsulator, wherein the first electrode, the second electrode, and theinsulator form a cavity, the second electrode forms an outlet passageextending from the cavity to a tip of the igniter assembly, the outletpassage has a substantially constant cross-sectional area along alongitudinal extent of the outlet passage from the cavity to the tip ofthe igniter assembly, a maximum cross-sectional area of the cavity isgreater than the substantially constant cross-sectional area of theoutlet passage, the cavity includes a converging section having across-sectional area that decreases continuously from the maximumcross-sectional area of the cavity to the outlet passage, the convergingsection extends to an interface between the cavity and the outletpassage, the converging section is formed only by the second electrode,the cavity includes a substantially constant cross-sectional areasection extending from the first electrode to the converging section,the substantially constant cross-sectional area section has asubstantially constant cross-sectional area substantially equal to themaximum cross-sectional area of the cavity, and the substantiallyconstant cross-sectional area section is formed only by the insulatorand the first electrode; wherein the outlet passage is the only fluidpassage extending from the cavity; and wherein the first electrode andthe second electrode are configured to ionize gas within the cavity inresponse to an electrical current applied to the first electrode or tothe second electrode.
 8. The igniter assembly of claim 7, wherein thefirst electrode comprises a center electrode, the second electrodecomprises an outer shell electrode disposed circumferentially about thecenter electrode, and the insulator is disposed radially between thecenter electrode and the outer shell electrode.
 9. The igniter assemblyof claim 7, wherein a longitudinal extent of the cavity is greater thana longitudinal extent of the outlet passage.